It would take 50 hours for the leak to empty the whole tank.
The reasoning behind that is because the pipe fills the tank with liquid in 5 hours, but due to the leak it takes 5.5 hours to fill the tank. So for every 5 hours the pipe leaks half an hour(.5) worth of liquid.
5 hours - .5 leaked
10 hours - 1
15h - 1.5
20h - 2
25h - 2.5
&
50h - 5